Hi, im running a PV1500 for mid/highs (either a pair of PV115's or a pair of older Hisys 2's depending on which band im with) and a Tapco J2500 for subs (2 x Tapco 6918's). We always have to push the PV1500 till the DDT led flickers to get enough volume for the vocals to be heard so i was wondering whether the PV1500 would be safe running in bridge mode for the mid/highs therefore giving 1500 watts @ 4 ohms headroom. 750 to each speaker right? Is the PV1500 safe running at 4 ohms bridge? Also am i right in thinking that the optimum power amp wattage for speakers is around 1.5 times the rated RMS for the the speaker? The 115's are rated 400 watts RMS and the Hisys 2's are rated 350 watts RMS so this setup should be safe right?

Would this setup be safe for the speakers and amp? I run the crossover (behringer CX2310) at a fairly high frequency, 200 hz, to try and keep as much of the low end out of the mid/tops as possible so amp/speakers shouldn't be working too hard.

My thinking is that using bridge mode at 4ohms the extra load this places on the amp should be more than offset by the fact i shouldn't have to drive it so hard to get the vocals to a high enough level and provide enough headroom for the screamo parts of our set.

Thanx for any advice/suggestions

Wayno.

Any takers? Is the PV1500 safe at 4 ohms bridge???

Wayne.

Did you look at the manual?

This bit seems to answer your question rather well:

Quote:

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BRIDGE MODE
The Bridge mode on stereo amplifiers is often misunderstood relating to actual operation and usage. In basic terms, when a 2-channel amplifier is operated in the Bridge mode, it is converted into a single-channel unit with a power rating equal to the sum of the power rating for each channel, at a load of twice that of the single-channel rating. For example, the PV 1500 is rated at 750 Watts RMS per channel into 2 Ohms. The Bridge rating is 1500 Watts RMS into 4 Ohms (minimum load). Bridge mode operation is accomplished by placing the MODE switch in the BRIDGE position, using only the BRIDGE Speakon® connector or the red binding posts for the output, and using the CHANNEL A input. All CHANNEL B input functions are defeated and serve no purpose now. Bridge mode operation can be used to drive sound distribution systems in very large public address applications. Another common use for the Bridge mode is in subwoofer applications where very high power levels are required to reproduce extremely low frequencies with adequate headroom. Such enclosures usually contain 2 or 4 loudspeakers to handle the power levels involved. For Bridge mode usage, the enclosure impedance must be 4 or 8 Ohms — never below 4 Ohms.

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I suspect that the main problem is that the speakers themselves aren't good enough. While their electronics are fine, I've always struggled to get a good sound with Peavey speakers - they have no real top end in my experience, just a harsh high midrange.

James.

--------------------
JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Thanks for the input guys, however that doesn't really answer my question. I know what bridge mode is, how to connect the speakers for that mode and the impedance levels etc. I have read the manual and in the bridge mode section it states that the amp will provide 1500w at 4 ohm bridge. However, in the specs sheet at the end of the manual there is no mention of 4 ohms bridge only 8 ohms bridge which gives me the impression they aren't overly confident in their product. Especially as it is only an entry level amp. After having read through countless threads on this and other forums about using bridge mode it's been said many times that certain entry level amps, although they claim to be safe to run in 4 ohms bridge actually struggle with it to the point of failure. What i was wondering was if anyone had any experience with this particular amp as i haven't found any thing so far. Yeah, i know that peavey speakers (especially these one's) aren't considered particularly high end, however, that is what we have. Just wondering whether using that amp in bridge for the mid/highs would be an effective way to get the best out of what we have?

Thanx or your reply tho guys,

Wayno.

OK

I never had any luck running the old Peavey CS- - - -X amps at 2ohms they kept overheating and cutting out, though 3.7ohms was OK.

I would hope the they've got better in the last 15 years or so, but I've not used them, so I can't tell you.

That probably doesn't help that much either!

Mark

Thanx for the reply Mark,

mmm think i'll just stick to using it at the standard 8 ohms a side and make sure the gain structure is as clean as possible through out the signal path. At least it won't be my fault if something blows :-) It's up to the drummer then, he can either stump up for a better PA or learn to lay back a bit.

Thanz for taking the time to help,

Wayno.

Hi Wayno,

It's always difficult if you operate PA's near their limits. As well as leaving lots of headroom in the mix, you need to keep them well within their limits (unlike obviously guitar amps), so I'm not surprised it's a problem. I bridged the bass bins in one of my setups, which was fine as they're non-directional - and they were never anything like near to max. I'd not bridge anything if I can help it, for the reasons you've discussed - plus a spare amp channel can get you out trouble.

But to what extent are you miking up your obviously enthusiastic drummer? Sounds like you could consider for most venues just giving him a bit of kick at around 90Hz and turning everything linked to him down if not off? Then reduce the bass to match and see what's left.

I realise this is standard live mixing procedure, so apologies if you tried this ages ago. But if this is the case, or your venues are too big for a mostly un-miked drummer, you do need to get a bigger rig, then operate it at 50% rather then 90...

Hi Hugh,

Yeah you are right about a spare channel getting you out of a hole. Having recently arrived late to a practice one of the others had set up the PA and wired up the monitor for the drummer wrong, Cue horrible noise and lots of acrid smoke from the front of the PV amp. So it's now currently in a mates house awaiting repair (he is a qualified tech and im assured he knows what he's doing so bit of luck there i suppose). Therefore the Tapco J2500 has been running the whole show at our most recent gigs. One side running both the mid/highs and the other channel running both the subs. Which i must add, it does very well. However it too is running full tilt to do this.

He is a very enthusiastic drummer im afraid. Recently he's calmed down a bit due to now using his own kit which "he" had to pay for but up until now he's managed to not have a cymbal last any more than six months before it literally tore into pieces! Breaks at least three sticks a session, just at practice i might add! Never breaks any skins though, ever??? He is however very technically gifted so i guess we've all just learn't to live with his volume. He only ever gets his kick drum mic'd at any gig, we only play the local pubs and bars and he's more than loud enough on his own for these. I think the biggest one we squeezed nearly 200 in and you couldn't move so they are not big venues at all. We use a speaker that i re-wired to use as a mic for his kick and i gotta say it sounds awesome. Really beefy and punchy too, really pleased with it cuz it was just an experiment after seeing it at the Foo's gig at wembley stadium the other year. Apart from the kick the only other stuff going through the PA is the bass guitar and 3 vocals,. And i try to EQ the vocals as separate as possible from the bass and kick so they're not all fighting for the same frequencies. Non of the kick and virtually non of the bass gets to the mid/high speakers. I have told the rest of the band before that as long as we keep having to run the PA flat out something WILL go pop at just the wrong time so after reading through what you said i'll make another point about it and see if i can convince them to agree to at least getting an amp with a bit more balls.

Thanx for your time and insight,

Wayno.

Tiny point of order?

Bridged mode effectively puts the amplifier outputs in series and thus the power output into any specified single channel Z is multipled theoretically by 4.

However, since each channel now "sees" only half the load value, as the book says, you must not load it below its minumum rated impedance.

Bridged operation used to be a bit notorious for stability issues, I dare say these have been sorted these days?

Dave.

Hi Wayno,

I like the speaker/mike idea...

I hope you don't have a bass guitarist who believes he can use single speaker home practice combo on stage "and DI it into the pa...." If so, THAT could be your real problem - as DI'd bass will take up far too much from your system, plus ruin your chances of any sensible vocal foldback.

Especially with a loud drummer, bass guitarists need at least 300 watts RMS - preferably 800, and suitable speakers (4x10 plus a reflex 15 or even 18 depending on music type). And this is just for un-reinforced stage sound - so the bass balances with the drums.

At your venues, and as bass is non directional and has a longer wavelength, you're going to get plenty of bass from a sensible backline rig without reinforcing it using your pa. If you're not miking up the drums, then you shouldn't mike the bass either.

But also remember, a pa provides "sound reinforcement", which for your gigs means vocals and vocal foldback, then possibly a touch of "thwack" for the kick around 90Hz, and even more possibly, a little "zing" from an overhead (but I wouldn't bother with that, for reasons of feedback etc).

But I'd start with just the vocals through your pa. I'd also buy a big stereo amp to replace what's gone down and run it stereo. Then get the other one repaired as spare...

Hi Dave. thanks for the reply,

So running 2 x 8 ohm speakers in parallel to a bridged amp is still producing a total load of 4 ohms, as would 2 x 8 ohm speakers run in parallel to one channel in normal mode provide a load of 4 ohms to that channel? Forgive me if im being thick but thats the way i think i understand it??? Bridge mode runs the 2 channels as one to give 4 times the output but only half the load so the way i understand it 4 ohms into bridge means that each channel effectively see's 2 ohms and the whole amp a total load of 4 ohms. Is that correct?

Thanx,


Wayno.

Thanks Hugh,

Yeah the speaker mic works a treat, had to suss some basic maths to figure out how to wire a simple pad to reduce the output cuz with the signal is way to high but once i'd sussed it got working a treat. The bass player has a 500w Hartke rig with a Hartke 4x10 cab so he's got plenty of stage volume, we mic him with an SM57 just to give him some "rumble" as he doesn't have an 18 or 15 cab to run in his rig. I also EQ out all of his bass frequencies above about 200hz so the PA is only giving him that "rumble" and nothing else. Would prefer not to have to lose that aspect of our sound as it does give us some quite impressing presence when we jump into a beefy song. However vocals are the most important part of the song and if we have to sacrifice some bass for that then so be it.

Will defo get them to consider looking for a more ballsy replacment and like you say, keep the PV1500 as a spare.

Thanx for your time,

Wanyo.

Quote waynogeoff:

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Hi Dave. thanks for the reply,

So running 2 x 8 ohm speakers in parallel to a bridged amp is still producing a total load of 4 ohms, as would 2 x 8 ohm speakers run in parallel to one channel in normal mode provide a load of 4 ohms to that channel? Forgive me if im being thick but thats the way i think i understand it??? Bridge mode runs the 2 channels as one to give 4 times the output but only half the load so the way i understand it 4 ohms into bridge means that each channel effectively see's 2 ohms and the whole amp a total load of 4 ohms. Is that correct?

Thanx,


Wayno.

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Err? Pretty much! Since the outputs are effectively in series, the same current must flow through both. Now, if you double the output voltage you therefore double the current through any specific load and therefore each amp section. It must therefore deliver that current at the same voltage as before: 2X current at same volts is equivalent to 1/2 the load Z.

Dave.

Thanks for the knowledge Dave. Always good to get a better understanding of the idea and how it works. Like i mentioned above im gonna stay away from bridge mode for now and see about a better amp to use in standard mode. Should be a better solution in the long run.

Thanx for your time and knowledge.

Wayno.

I only recently found aout about this 2 ohm deal. I have been running 2 bins daisy chained off the bridge mono channel for over 3 three years. Now and again the amp will overheat and go into protection but I thought I was just overdriving it. Now it turns out I have been running each amp into 2 ohms.

Although this is counter-intuitive you would actually be better off with two 8 ohm bins running off EACH channel in stereo mode with a 4 ohm load on each channel than two 8 ohm bins daisy chained off the bridge channel effectively putting each channel under a 2 ohm load ???

Would the extra cone area of option one produce more volume, or the 2 ohm power of option 2 ???

The more I learn the more questions I have !!!

ReetMonkey!
It breaks down like this.
Say you have an amp specced at 300watts per channel into 8 Ohms? If all stayed the same (never does, quite) such an amp would put out 600W each channel into 4 Ohms and in many cases 4 Ohms would be the lowest load Z you could safely use. So, now that we know that bridge connecting an amp effectively halves the impedance "seen" by each channel we must not connect a load smaller than 8Ohms to such an amp if used in bridge mode.

As far as speakers are concerned no, more cone area does not mean a higher SPLs (that would lead to a perpetual motion machine!) but more speakers can handle more watts so they might not go into thermal compression so early, if at all and thus the ULTIMATE SPL could be higher. This is especially true of guitar speakers where they tend to have their nuts driven off.

Dave.

Right!

Just to clarify, I use a Numark Dimension 4 amp to power my bins.

The amp is rated at 412 Watts RMS @ 8 Ohms per channel stereo!
or
1900 Watts RMS @ 4 ohms bridged mono!

I have two Cerwin Vega 118s bins rated at 500 watt program @ 8 ohms.

If I run them stereo they only get 412 watts each, but if I link them they get 1900 watts between them, thats 950 each! But the amp has now gone from 8 ohms per channel all the way down to 2 ohms to achieve this?

Am I right ???

I should add that the amp has done about 250 2 hour gigs running in bridge mode and is still going strong!!! Should I be running it stereo instead?